The stars we observe vary in both color and brightness. The brightness of a star depends both on its mass and on its distance. And the color of the glow depends on the temperature on its surface. The coolest stars are red. And the hottest ones have a bluish tint. White and blue stars are the hottest, their temperature is higher than the temperature of the Sun. Our star, the Sun, belongs to the class of yellow stars.
How many stars are there in the sky?
It is almost impossible to calculate even approximately the number of stars in the part of the Universe known to us. Scientists can only say that there may be about 150 billion stars in our Galaxy, which is called the Milky Way. But there are other galaxies! But people know much more accurately the number of stars that can be seen from the surface of the Earth with the naked eye. There are about 4.5 thousand such stars.
How are stars born?
If the stars light up, does that mean someone needs it? In the endless space there are always molecules of the simplest substance in the Universe - hydrogen. Somewhere there is less hydrogen, somewhere more. Under the influence of mutual attractive forces, hydrogen molecules are attracted to each other. These attraction processes can last for a very long time - millions and even billions of years. But sooner or later, the hydrogen molecules are attracted so close to each other that a gas cloud forms. With further attraction, the temperature in the center of such a cloud begins to rise. Another millions of years will pass, and the temperature in the gas cloud may rise so much that a thermonuclear fusion reaction will begin - hydrogen will begin to turn into helium and a new star will appear in the sky. Any star is a hot ball of gas.
The lifespan of stars varies significantly. Scientists have found that the greater the mass of a newborn star, the shorter its lifespan. The lifespan of a star can range from hundreds of millions of years to billions of years.
Light year
A light year is the distance covered in a year by a beam of light traveling at a speed of 300 thousand kilometers per second. And there are 31,536,000 seconds in a year! So, from the closest star to us, called Proxima Centauri, a beam of light travels for more than four years (4.22 light years)! This star is 270 thousand times farther from us than the Sun. And the rest of the stars are much further away - tens, hundreds, thousands and even millions of light years from us. This is why stars appear so small to us. And even in the most powerful telescope, unlike planets, they are always visible as dots.
What is a "constellation"?
Since ancient times, people have looked at the stars and seen in the bizarre figures that form groups of bright stars, images of animals and mythical heroes. Such figures in the sky began to be called constellations. And, although in the sky the stars included by people in this or that constellation are visually close to each other, in outer space these stars can be located at a considerable distance from each other. The most famous constellations are Ursa Major and Ursa Minor. The fact is that the constellation Ursa Minor includes the Polar Star, which is pointed to by the north pole of our planet Earth. And knowing how to find the North Star in the sky, any traveler and navigator will be able to determine where north is and navigate the area.
Supernovae
Some stars, at the end of their lives, suddenly begin to glow thousands and millions of times brighter than usual, and eject huge masses of matter into the surrounding space. It is commonly said that a supernova explosion occurs. The glow of the supernova gradually fades and eventually only a luminous cloud remains in the place of such a star. A similar supernova explosion was observed by ancient astronomers in the Near and Far East on July 4, 1054. The decay of this supernova lasted 21 months. Now in the place of this star there is the Crab Nebula, known to many astronomy lovers.
To summarize this section, we note that
V. Types of stars
Basic spectral classification of stars:
Brown dwarfs
Brown dwarfs are a type of star in which nuclear reactions could never compensate for the energy lost to radiation. For a long time, brown dwarfs were hypothetical objects. Their existence was predicted in the middle of the 20th century, based on ideas about the processes occurring during the formation of stars. However, in 2004, a brown dwarf was discovered for the first time. To date, quite a lot of stars of this type have been discovered. Their spectral class is M - T. In theory, another class is distinguished - designated Y.
White dwarfs
Soon after the helium flash, carbon and oxygen “ignite”; each of these events causes a strong restructuring of the star and its rapid movement along the Hertzsprung-Russell diagram. The size of the star's atmosphere increases even more, and it begins to intensively lose gas in the form of scattering streams of stellar wind. The fate of the central part of the star depends entirely on its initial mass: the core of the star can end its evolution as a white dwarf (low-mass stars), if its mass in the later stages of evolution exceeds the Chandrasekhar limit - as a neutron star (pulsar), if the mass exceeds The Oppenheimer-Volkov limit is like a black hole. In the last two cases, the completion of the evolution of stars is accompanied by catastrophic events - supernova explosions.
The vast majority of stars, including the Sun, end their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a hundred times, and the density becomes a million times higher than the density of water, the star is called a white dwarf. It is deprived of energy sources and, gradually cooling down, becomes dark and invisible.
Red giants
Red giants and supergiants are stars with a fairly low effective temperature (3000 - 5000 K), but with enormous luminosity. The typical absolute magnitude of such objects is 3m-0m (luminosity class I and III). Their spectrum is characterized by the presence of molecular absorption bands, and the maximum emission occurs in the infrared range.
Variable stars
A variable star is a star whose brightness has changed at least once in its entire observation history. There are many reasons for variability and they can be associated not only with internal processes: if the star is double and the line of sight lies or is at a slight angle to the field of view, then one star, passing through the disk of the star, will eclipse it, and the brightness may also change if the light from the star will pass through a strong gravitational field. However, in most cases, variability is associated with unstable internal processes. The latest version of the general catalog of variable stars adopts the following division:
Eruptive variable stars- these are stars that change their brightness due to violent processes and flares in their chromospheres and coronas. The change in luminosity usually occurs due to changes in the envelope or mass loss in the form of variable-intensity stellar wind and/or interaction with the interstellar medium.
Pulsating Variable Stars are stars that exhibit periodic expansion and contraction of their surface layers. Pulsations can be radial or non-radial. Radial pulsations of a star leave its shape spherical, while non-radial pulsations cause the star's shape to deviate from spherical, and neighboring zones of the star may be in opposite phases.
Rotating Variable Stars- these are stars whose brightness distribution over the surface is non-uniform and/or they have a non-ellipsoidal shape, as a result of which, when the stars rotate, the observer records their variability. Inhomogeneities in surface brightness can be caused by spots or temperature or chemical irregularities caused by magnetic fields whose axes are not aligned with the star's rotation axis.
Cataclysmic (explosive and nova-like) variable stars. The variability of these stars is caused by explosions, which are caused by explosive processes in their surface layers (novae) or deep in their depths (supernovae).
Eclipsing binary systems.
Optical variable binary systems with hard X-ray emission
New Variable Types- types of variability discovered during the publication of the catalog and therefore not included in already published classes.
New
A nova is a type of cataclysmic variable. Their brightness does not change as sharply as that of supernovae (although the amplitude can be 9m): a few days before the maximum, the star is only 2m fainter. The number of such days determines which class of novae the star belongs to:
Very fast if this time (denoted as t2) is less than 10 days.
Fast - 11
There is a dependence of the maximum brightness of the nova on t2. Sometimes this dependence is used to determine the distance to a star. The flare maximum behaves differently in different ranges: when in the visible range there is already a decline in radiation, in the ultraviolet it is still growing. If a flash is also observed in the infrared range, then the maximum will be reached only after the glare in the ultraviolet subsides. Thus, the bolometric luminosity during a flare remains unchanged for quite a long time.
In our Galaxy, two groups of novae can be distinguished: new disks (on average, they are brighter and faster), and new bulges, which are a little slower and, accordingly, a little fainter.
Supernovae
Supernovae are stars that end their evolution in a catastrophic explosive process. The term “supernovae” was used to describe stars that flared up much (by orders of magnitude) more powerfully than the so-called “novae.” In fact, neither one nor the other are physically new; existing stars always flare up. But in several historical cases, those stars flared up that were previously practically or completely invisible in the sky, which created the effect of the appearance of a new star. The type of supernova is determined by the presence of hydrogen lines in the flare spectrum. If it is there, then it is a type II supernova, if not, then it is a type I supernova.
Hypernovae
Hypernova - the collapse of an exceptionally heavy star after there are no more sources left in it to support thermonuclear reactions; in other words, it is a very large supernova. Since the early 1990s, stellar explosions have been observed so powerful that the force of the explosion exceeded the power of an ordinary supernova by about 100 times, and the energy of the explosion exceeded 1046 joules. In addition, many of these explosions were accompanied by very strong gamma-ray bursts. Intensive study of the sky has found several arguments in favor of the existence of hypernovae, but for now hypernovae are hypothetical objects. Today the term is used to describe the explosions of stars with masses ranging from 100 to 150 or more solar masses. Hypernovae could theoretically pose a serious threat to the Earth due to a strong radioactive flare, but at present there are no stars near the Earth that could pose such a danger. According to some data, 440 million years ago there was a hypernova explosion near the Earth. It is likely that the short-lived nickel isotope 56Ni fell to Earth as a result of this explosion.
Neutron stars
In stars more massive than the Sun, the pressure of degenerate electrons cannot contain the compression of the core, and it continues until most of the particles turn into neutrons, packed so tightly that the size of the star is measured in kilometers, and its density is 280 trillion. times the density of water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.
To the question, are the stars (which are in the sky) hot or cold? given by the author Catherine the best answer is All stars are divided into 7 classes by temperature and, accordingly, by spectral type: OBAFGKM. The hottest are blue O (from 30 to 60 thousand degrees), the coldest are orange-red M (from 3 to 4.5 thousand degrees).
The sequence of spectral classes is easy to remember using the phrase
"One shaved Englishman chewed dates like carrots."
Here the first letter of each word, in English transcription, is the name of the spectral class in the order of their sequence.
Our Sun is class G (more precisely, G2 - each class also has numerical subclasses).
Answer from philosopher[guru]
They're hot, that's why they're stars!
Answer from Koroteev Alexander[guru]
Everything is in comparison.
If you compare their temperature (even the surface) with what is “comfortable” for a person, they are all VERY hot.
If they are shining, it means they are hot - because they shine due to thermal radiation, and to emit in the optical range, thousands of degrees are needed.
Compared to the Sun, most stars visible to the eye are larger and hotter than the Sun.
If you compare with each other, you can distinguish those that are hotter and those that are colder. The latter are not that cold - well, like boiling water compared to boiling oil. The first is colder, of course, but I haven’t heard of anyone being scalded and glad that it wasn’t oil.
>^.^<
Answer from Landrail[expert]
You still can’t tell with certainty whether a star is “cold” or “hot” by eye; this is due to the Doppler effect. In other words, the star may be moving away from you or towards you, and depending on this, the “visible color of the star” may be redder or bluer, respectively. True, it is worth noting that the shift in the spectral line may not be noticeable to the eye, but this will be enough to make a slight error of a couple of thousand degrees, or even more than a dozen. And certainly if you “turn off” the sun, they will not warm you, so the stars in the sky are colder than the coldest toilet seat you have ever sat on. =)
Answer from Neurosis[guru]
if it is a meteorite, it is hot due to the rapid movement. in general, the hottest “star” is the sun, and the rest are cold in comparison.
Answer from Summer[guru]
The color of stars is determined by their spectral class. There are six spectral classes. I name four main ones:
The coldest red stars are colder than our sun - on the surface the temperature is about 4 thousand degrees (our sun has 6 thousand - it is yellow). The hottest white stars are up to 10 thousand temperatures on the surface. Blue ones are a little cooler.
Answer from Not Touching[guru]
With a red tint - cold, with a blue tint - hot
Answer from Art[guru]
cold.... the brighter the star, the colder it is...
Answer from Yoman Mikhashchuk[active]
Very Hot Plasma
Answer from Vladimir buhvestov[expert]
All the stars in the sky are cold
Answer from Marco Polo[guru]
The stars are cold.
Here is an excerpt as proof:
"And the stars were knocking in the sky,
Like rain on black glass,
And, rolling down, they cooled down
Her hot face..."
It is said in such a way that you believe every detail, and if the stars cool down, it means that someone needs it...
And at the other extreme, these are stars many times cooler than the Sun, the so-called red stars. Recently, astrophysicists were lucky enough to answer the question - which star is the coldest. This is the star CFBDS0059 with a temperature of 350 (three hundred and fifty!) degrees Celsius!
It is incredible, but true, that the surface of this sub-star is colder than the surface of Venus. It turns out that astronomers can answer the question of how this can be. However, even red dwarf stars have temperatures of 2,000 – 3,000 degrees. Well, it turns out that cooler, and therefore fainter, stars may exist. Such stars are called brown dwarfs. But, to be honest, these are still not exactly stars, in their classical sense. This is rather a special class of celestial bodies.
It’s so difficult to draw a clear line between stars and planets! Brown dwarfs are a special class of objects that are an intermediate link between stars and planets. Young brown dwarfs are stars. Old brown dwarfs are planets of the Jupiter group and other giant planets.
According to the theory of the structure and life of stars, it is believed that the lower limit of mass for stars is considered to be 80 masses of Jupiter, because with a lower mass they will not be able to begin, and once they begin to take a long time, thermonuclear reactions, which are the basis for the existence of any star. This thermonuclear reaction supplies stars with energy. However, according to scientists, brown dwarfs burn not ordinary hydrogen, but heavy hydrogen - deuterium. It doesn’t last very long, and therefore the star burns safely for some time, but then begins to quickly cool down, apparently turning into a planet of the Jupiter class.
For the emergence of a brown dwarf, just nothing is enough - 13 Jupiter masses. Astronomers knew about the existence of two types of brown dwarfs - L and T classes. L dwarfs are hotter than their cousins, T dwarfs. It was found that the discovered cold star belongs to a completely new, previously existing only in paper theory - class Y.
The star CFBDS0059 has a mass of 15 to 30 times the mass of Jupiter and is located at a rather ridiculous distance from us, by the standards of the Universe - 40 light years. The peculiarity of this cool star (Y-class brown dwarf) is that due to its low temperature, the Y-dwarf CFBDS0059 is extremely dim and emits mainly light in the infrared region of the spectrum.
It is impossible to see this small and extremely cold (for a star) object in an amateur telescope, and even more so in a homemade telescope. During the discovery, scientists used large telescopes with mirror diameters from 8 to 10 meters. Spectral absorption lines of methane were found in the spectrum of the newly discovered brown dwarf, which, in the overall picture with other data, convinced astronomers that the discovery was a star, not a planet, with a record low temperature on its surface. So, the Dark and Cold Star has been discovered - a Y-class brown dwarf, with a surface temperature of only 350 degrees Celsius!
Paradox: cold stars
When we talk about stars, we usually mean celestial bodies heated to incredibly high temperatures. And the temperatures there are truly gigantic. After all, even the surface of the closest star to us - the Sun, with a temperature of 6000 degrees, can be considered only slightly heated in comparison with those “torches” of the Universe, the temperature of which reaches several tens and hundreds of thousands of degrees. Such “hot” objects include white dwarfs with temperatures of 200,000 degrees.
It's hard to believe, but it turns out that there are stars that are many times colder than the Sun. These are the so-called brown dwarfs. We will return to them in Chapter 7.
At one time, the record holder in this temperature category was a star designated in catalogs as CFBDS0059. The temperature of this star, according to various sources, ranges from 180 to 350 degrees Celsius. And this is almost the same for a star as Antarctica is for the Earth.
Brown dwarf in the constellation Bootes
Astronomers call stars with such low temperatures brown dwarfs. In fact, this is a special class of celestial bodies, occupying an intermediate position between stars and planets. Moreover, in the early stages of their evolution, that is, in their youth, brown dwarfs are stars. When they “grow old,” they move to the group of planets like Jupiter, that is, giant planets.
Experts often call brown dwarfs “stars that never happened.” This is due to the fact that although thermonuclear reactions take place in them, they cannot compensate for the energy spent on radiation and therefore cool down over time. But they cannot be called planets for the reason that they do not have a clear morphological structure: they have neither a core nor a mantle and are dominated by convection currents. And since such a structure is characteristic of stars, brown dwarfs ended up in this category of celestial bodies.
In accordance with the generally accepted theory of the structure and evolution of stars, it is generally accepted that a celestial body becomes a sun if its weight reaches 80 times the mass of Jupiter. This is due to the fact that with a lower mass, thermonuclear reactions that provide it with the necessary energy will not be able to take place in the star.
For a brown dwarf to appear, a celestial object only needs to have a weight equal to 13 Jupiter masses. By cosmic standards, this is not a very large value.
Since 1995, when the existence of these cosmic bodies was confirmed by real research, more than a hundred of them have already been discovered. Scientists divided them all into two groups: hotter dwarfs belong to the L-class, and cooler ones belong to the T-class.
But the newly discovered cold star CFBDS0059 did not find a place in this classification, and it had to be allocated a separate “room” - the Y-class.
The mass of this star is from 15 to 30 times the mass of Jupiter. It is located at a distance of 40 light years from Earth. The peculiarity of this star is that, due to its low temperature, it is extremely dim, and its radiation is recorded mainly in the infrared region of the spectrum.
But very little time passed, and in 2011, astronomers discovered an even cooler brown dwarf. They saw it using a ten-meter telescope located on the island of Mauna Kea. Moreover, the signal from this celestial object was so weak that it was difficult to isolate it from the general cosmic noise.
The newly discovered brown dwarf received the classification number CFBDSIR J1458+1013B. Unlike its previously discovered “ice” brother, it is part of a pair system. His partner is also a brown dwarf, but already quite ordinary. This structure is located at a distance of 75 light years from Earth.
The temperature of the new record holder fluctuates somewhere in the region of 60-135 degrees Celsius. This means that this brown dwarf may contain water, and in a liquid state.
True, hot water vapor was also recorded in the atmosphere of brown dwarfs before. But on this incredibly cold dwarf, scientists suggest, it may even be in the form of clouds.
From the book Encyclopedic Dictionary (P) author Brockhaus F.A.Paradox Paradox (para-dokew-seem) is an opinion that diverges from the generally accepted one. P. can express both a true opinion and a false one, depending on what is generally accepted. The desire for paradoxical statements, characteristic of many authors, often characterizes
From the book In the beginning there was a word. Aphorisms authorParadox in music Paradox in music - everything exquisite, strange, as well as the names of singers or instrumentalists who won championships at the Olympic Games
From the book Everything is Science. Aphorisms author Dushenko Konstantin VasilievichParadox and banality Paradox: a logical statement about an absurd reality. Henryk Jagodzinski (b. 1928), Polish satirist A paradox is two ends of one truth. Wladyslaw Grzegorczyk, Polish aphorist The road to truth is paved with paradoxes. Oscar Wilde (1854–1900),
From the book Great Soviet Encyclopedia (GI) by the author TSBPARADOX Paradox: a logical statement about an absurd reality. Henryk Jagodzinski We speak of paradoxes because of the impossibility of finding truths that are not banal. Jean Condorcet Any precise definition of the world will be a paradox. Stanislav Jerzy Lec Paradox –
From the book Great Soviet Encyclopedia (GR) by the author TSB From the book Great Soviet Encyclopedia (ZE) by the author TSB From the book Great Soviet Encyclopedia (OL) by the author TSB From the book Great Soviet Encyclopedia (PA) by the author TSB From the book Great Soviet Encyclopedia (FO) by the author TSB From the book A Million Dishes for Family Dinners. Best Recipes author Agapova O. Yu. From the book The Complete Illustrated Encyclopedia of Our Misconceptions [with illustrations] author From the book The Complete Illustrated Encyclopedia of Our Misconceptions [with transparent pictures] author Mazurkevich Sergei Alexandrovich From the book Great Encyclopedia of Canning author Semikova Nadezhda AleksandrovnaFools have cold ears. Absolutely all people, regardless of their mental abilities, have ear temperatures lower than body temperature by 1.5–2
From the book Philosophical Dictionary author Comte-Sponville AndreCold Feet Some parents often panic when their young children, despite being kept warm (and even too warm), constantly have cold hands and feet. And the parents themselves, and numerous “advisers” in the person of grandparents, relatives and friends
There are so many strange, amusing and interesting things around us, but someone else manages to get bored.
Beautiful and amazing space
Space is beautiful and quite amazing. Planets orbit stars that die and go out again, and everything in the galaxy revolves around a supermassive black hole that slowly sucks in anything that gets too close. But sometimes space throws up such strange things that you'll twist your mind into a pretzel trying to figure it out...
Red Square Nebula
Objects in space are, for the most part, quite round. Planets, stars, galaxies and the shape of their orbits all resemble a circle. But the Red Square Nebula, an interestingly shaped cloud of gas, hmm, square. Of course, astronomers were very, very surprised, since objects in space should not be square.
In fact, it's not exactly a square. If you look closely at the image, you will notice that the cross-section of the shape is formed by two cones at the point of contact. But then again, there aren't many cones in the night sky.
The hourglass-shaped nebula glows very brightly because there is a bright star at its very center, where the cones touch. It is possible that this star exploded and went supernova, causing the rings at the base of the cones to glow more intensely.
Galaxy collisions
In space, everything is constantly moving - in orbit, around its axis, or simply rushing through space. For this reason—and because of the incredible force of gravity—galaxies collide constantly. This may not surprise you - just look at the Moon and realize that space loves to keep small things close to big ones. When two galaxies containing billions of stars collide, it's a local disaster, right?
In fact, in galaxy collisions, the likelihood of two stars colliding is virtually zero. The fact is that in addition to the fact that space itself is large (and galaxies too), it is also quite empty in itself. That is why it is called “outer space”. Although our galaxies appear solid from a distance, remember that the nearest star to us is 4.2 light years away. It's very far away.
Pillars of Creation
As Douglas Adams once wrote, “space is big. Actually big. You can’t even imagine how mind-bogglingly big it is.” We all know that the unit of measurement used to measure distances in space is the light year, but few people think about what that means. A light year is such a long distance that light, the fastest-moving thing in the universe, takes only a year to travel that distance.
This means that when we look at objects in space that are truly distant, like the Pillars of Creation (the formations in the Eagle Nebula), we are looking back in time. How does this happen? Light from the Eagle Nebula takes 7,000 years to reach Earth and we see it as it was 7,000 years ago because what we see is reflected light.
The consequences of this looking into the past are very strange. For example, astronomers believe that the Pillars of Creation were destroyed by a supernova about 6,000 years ago. That is, these Pillars simply no longer exist. But we see them.
Horizon problem
Space is a complete mystery, no matter where you look. For example, if we look at a point in the east of our sky and measure the background radiation, and then do the same at a point in the west, which is separated from the first by 28 billion light years, we will see that the background radiation at both points is the same temperature.
This seems impossible because nothing can travel faster than light, and even light would take too long to travel from one point to another. How could the microwave background stabilize almost uniformly throughout the universe?
This could be explained by the theory of inflation, which suggests that the universe stretched out over large distances immediately after the Big Bang. According to this theory, the Universe was not formed by stretching its edges, but space-time itself was stretched out like chewing gum in a fraction of a second.
In this infinitely short time in this space, a nanometer covered several light years. This does not contradict the law that nothing can move faster than the speed of light, because nothing moved. It just expanded.
Think of the original universe as a single pixel in an image editing program. Now scale the image by a factor of 10 billion. Since the entire point consists of the same material, its properties - including temperature - are uniform.
How a black hole will kill you
Black holes are so massive that material begins to behave strangely in close proximity to them. One can imagine that being sucked into a black hole means spending the rest of eternity (or wasting the remaining air) screaming hopelessly in a tunnel of the void. But don’t worry, the monstrous gravity will deprive you of this hopelessness.
The force of gravity is stronger the closer you are to its source, and when the source is such a powerful body, values can change dramatically even over short distances - say, the height of a person.
If you fall into a black hole feet first, the force of gravity on your legs will be so strong that you will see your body stretched into a spaghetti of lines of atoms that are pulled into the very center of the hole. You never know, maybe this information will be useful to you when you want to dive into the belly of a black hole.
Brain Cells and the Universe
Recently, physicists created a simulation of the beginning of the universe, which began with the Big Bang and the sequence of events that led to what we see today. A bright yellow cluster of densely packed galaxies in the center and a “network” of less dense galaxies, stars, dark matter and so on.
Model of the large-scale structure of space
At the same time, a student from Brandeis University was studying the interconnection of neurons in the brain by looking at thin layers of mouse brain under a microscope. The image he received contained yellow neurons connected by a red “network” of connections. Doesn't remind you of anything?
Neurons of the brain
The two images, although very different in scale (nanometers and light years), are strikingly similar. Is this just a simple case of fractal recursion in nature, or is the universe really just a brain cell inside another huge universe?
Missing baryons
According to the Big Bang theory, the amount of matter in the universe will eventually create enough gravitational pull to slow the expansion of the universe to a stop.
However, baryonic matter (what we see - stars, planets, galaxies and nebulae) makes up only 1 to 10 percent of all the matter that there should be. Theorists balanced the equation with hypothetical dark matter (which we cannot observe) to save the day.
Every theory that tries to explain the strange absence of baryons comes up empty. The most common theory is that the missing matter consists of the intergalactic medium (dispersed gas and atoms floating in the voids between galaxies), but even so, we are still left with a mass of missing baryons.
So far we have no idea where most of the matter that should actually be is.
Cold stars
No one doubts that stars are hot. This is as logical as the fact that snow is white and two and two make four. When visiting a star, we would worry more about not getting burned than about not freezing—in most cases.
Brown dwarfs are stars that are quite cool by stellar standards. Recently, astronomers discovered a type of star called Y-dwarfs, which are the coolest subtype of stars in the brown dwarf family.
Y dwarfs are cooler than the human body. At a temperature of 27 degrees Celsius, you can safely touch such a brown dwarf, unless its incredible gravity turns you to mush.
These stars are damn hard to detect because they emit virtually no visible light, so you can only look for them in the infrared spectrum. There are even rumors that brown and Y-dwarfs are the same “dark matter” that has disappeared from our Universe.
The solar corona problem
The further an object is from a heat source, the colder it is. That's why it's strange that the surface temperature of the Sun is about 2760 degrees Celsius, but its corona (sort of like its atmosphere) is 200 times hotter.
Even if there may be some processes that explain the temperature difference, none of them can explain such a large difference.
Scientists believe that this has something to do with small patches of magnetic field that appear, disappear and move across the surface of the Sun. Because the magnetic lines cannot cross each other, the inclusions rearrange themselves every time they get too close, a process that heats up the corona.
While this explanation may seem neat, it is far from elegant. Experts can't agree on how long these inclusions last, let alone the processes by which they might heat the corona. Even if the answer to the question lies there, no one knows what causes these random flecks of magnetism to appear in the first place.
Eridani black hole
The Hubble Deep Space Field is an image taken by the Hubble Telescope of thousands of distant galaxies. However, when we look into the "empty" space in the region of the constellation Eridanus, we see nothing. At all. Just a black void stretching across billions of light years.
Almost any “emptiness” in the night sky returns images of galaxies, albeit blurry, but existing. We have several methods that help identify what might be dark matter, but they also leave us empty-handed as we stare into the void of Eridani.
One controversial theory suggests that the void contains a supermassive black hole around which all nearby galaxy clusters orbit, and this high-speed rotation is combined with the "illusion" of an expanding universe. Another theory suggests that all matter will someday stick together to form galaxy clusters, and that drifting voids will eventually form between the clusters.
But that doesn't explain the second void astronomers have discovered in the southern night sky, this time about 3.5 billion light-years wide. It is so vast that even the Big Bang theory has difficulty explaining it, since the Universe did not exist long enough for such a huge void to form through normal galactic drift.
